Metal-Organic-Framework-Decorated Carbon Nanofibers with Enhanced Gas Sensitivity When Incorporated into an Organic Semiconductor-Based Gas Sensor

Advancements in MOF-based resistive gas sensors: synthesis methods and applications for toxic gas detection

Gas sensors are essential tools for safeguarding public health and safety because they allow the detection of hazardous gases. To advance gas-sensing technologies, novel sensing materials with distinct properties are needed. Metal-organic frameworks (MOFs) hold great potential because of their extensive surface areas, high porosity, unique chemical properties, and capabilities for preconcentration and molecular sieving. These attributes make MOFs highly suitable for designing and creating innovative resistive gas sensors. This review article examines resistive gas sensors made from pristine, doped, decorated, and composite MOFs. The first part of the review focuses on the synthesis strategies of MOFs, while the second part discusses MOF-based resistive gas sensors that operate based on changes in resistance.

Mining for Metal-Organic Systems: Chemistry Frontiers of Th-, U-, and Zr-Materials

The conceptual framework presented in this Perspective overviews the design principles of innovative thorium-based materials that could address urgent needs of the medicinal, nuclear energy, and waste remediation sectors from the lens of zirconium and uranium analogs. We survey the intersections of Zr, Th, and U chemistry with a focus on how the intrinsic behavior of each metal translates to broader material properties, including, but not limited to, structural and topological diversity, preferential metal-ligand binding, and reactivity. On the example of several classes of materials, including organometallic complexes, polyoxometalates, and the primary focus of this Perspective, metal-organic frameworks (MOFs), the design principles that govern the preparation of Zr-, Th-, and U-compounds, including oxophilicity, variation in oxidation states, and stable coordination environments have been considered. Further, we highlight how the impact of the mentioned variables may shift throughout the progression from discrete molecular systems to extended structures. We discuss the common assumption that zirconium-organic materials are typically considered a close analog of thorium-based congeners in areas such as material design and preparation. Through consideration of fundamental chemistry principles, we shed light on the relationships between Zr-, Th-, and U-based materials and highlight how a critical analysis of their distinct properties can be used to target a desired material performance. As a result, we provide a detailed understanding of Th-based materials chemistry by anchoring their fundamental properties between two well-studied reference points, zirconium- and uranium-containing analogs.

Interface Defects and Carrier Regulation in MOF-Derived Co3O4/In2O3 Composite Materials for Enhanced Selective Detection of HCHO

Gas sensors for real-time monitoring of low HCHO concentrations have promising applications in the field of health protection and air treatment, and this work reports a novel resistive gas sensor with high sensitivity and selectivity to HCHO. The MOF-derived hollow In2O3 was mixed with ZIF-67(Co) and calcined twice to obtain a hollow Co3O4/In2O3 (hereafter collectively termed MZO-6) composite enriched with oxygen vacancies, and tests such as XPS and EPR proved that the strong interfacial electronic coupling increased the oxygen vacancies. The gas-sensitive test results show that the hollow composite MZO-6 with abundant oxygen vacancies has a higher response value (11,003) to 10 ppm of HCHO and achieves a fast response/recovery time (11/181 s) for HCHO at a lower operating temperature (140 °C). The MZO-6 material significantly enhances the selectivity to HCHO and reduces the interference of common pollutant gases such as ethanol, acetone, and xylene. There is no significant fluctuation of resistance and response values in the 30-day long-term stability test, and the material has good stability. The synergistic effect of the heterostructure and oxygen vacancies altered the formaldehyde adsorption intermediate pathway and reduced the reaction activation energy, enhancing the HCHO responsiveness and selectivity of the MZO-6 material.

Room-temperature response of MOF-derived Pd@PdO core shell/γ-Fe2O3 microcubes decorated graphitic carbon based ultrasensitive and highly selective H2 gas sensor

With the current upsurge in hydrogen economies all over the world, an increased demand for improved chemiresistive H2 sensors that are highly responsive and fast acting when exposed to gases is expected. Owing to safety concerns about explosive and highly flammable H2 gas, it is important to develop resistive sensors that can detect the leakage of H2 gas swiftly and selectively. Currently, interest in metal-organic frameworks (MOFs) for gas-sensor applications is increasing due to their open-metal sites, large surface area, and unique surface morphologies. In this research, a highly selective and sensitive H2-sensor was established based on graphitic carbon (GC) anchored spherical Pd@PdO core-shells over γ-Fe2O3 microcube (Pd@PdO/γ-Fe2O3@GC which is termed as S3) heterostructure materials. The combined solvothermal followed by controlled calcination-assisted S3 exhibited a specific morphology with the highest surface area of 79.12 m2 g-1, resulting in fast response and recovery times (21 and 29 s, respectively), and excellent sensing performance (ΔR/R0∼ 96.2 ± 1.5), outstanding long-term stability, and a 100 ppb detection limit when detecting H2-gas at room temperature (mainly in very humid surroundings). This result proves that adsorption sites provided by S3 can promote surface reactions (adsorption and desorption) for ultrasensitive and selective H2gas sensors.

Wearable Nano-Based Gas Sensors for Environmental Monitoring and Encountered Challenges in Optimization

With a rising emphasis on public safety and quality of life, there is an urgent need to ensure optimal air quality, both indoors and outdoors. Detecting toxic gaseous compounds plays a pivotal role in shaping our sustainable future. This review aims to elucidate the advancements in smart wearable (nano)sensors for monitoring harmful gaseous pollutants, such as ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), ozone (O3), hydrocarbons (CxHy), and hydrogen fluoride (HF). Differentiating this review from its predecessors, we shed light on the challenges faced in enhancing sensor performance and offer a deep dive into the evolution of sensing materials, wearable substrates, electrodes, and types of sensors. Noteworthy materials for robust detection systems encompass 2D nanostructures, carbon nanomaterials, conducting polymers, nanohybrids, and metal oxide semiconductors. A dedicated section dissects the significance of circuit integration, miniaturization, real-time sensing, repeatability, reusability, power efficiency, gas-sensitive material deposition, selectivity, sensitivity, stability, and response/recovery time, pinpointing gaps in the current knowledge and offering avenues for further research. To conclude, we provide insights and suggestions for the prospective trajectory of smart wearable nanosensors in addressing the extant challenges.

Recent progress in 1D MOFs and their applications in energy and environmental fields

Metal organic frameworks (MOFs) are porous coordination polymers with adjustable nanostructure, high porosity and large surface areas. These features make MOFs, their derivates and composites all delivered remarkable potential in energy and environmental fields, such as rechargeable batteries, supercapacitors, catalysts, water purification and desalination, gas treatment, toxic matter degradation, etc. In particular, one-dimensional (1D) MOFs have generated extensive attention due to their unique 1D nanostructures. To prepare 1D MOF nanostructures, it is necessary to explore and enhance synthesis routes. In this review, the preparation of 1D MOF materials and their recent process applied in energy and environmental fields will be discussed. The relationship between MOFs' 1D morphologies and the properties in their applications will also be analyzed. Finally, we will also summary and make perspectives about the future development of 1D MOFs in fabrication and applications in energy and environmental fields.

Recent Progress in Gas Sensors Based on P3HT Polymer Field-Effect Transistors

In recent decades, the rapid development of the global economy has led to a substantial increase in energy consumption, subsequently resulting in the emission of a significant quantity of toxic gases into the environment. So far, gas sensors based on polymer field-effect transistors (PFETs), a highly practical and cost-efficient strategy, have garnered considerable attention, primarily attributed to their inherent advantages of offering a plethora of material choices, robust flexibility, and cost-effectiveness. Notably, the development of functional organic semiconductors (OSCs), such as poly(3-hexylthiophene-2,5-diyl) (P3HT), has been the subject of extensive scholarly investigation in recent years due to its widespread availability and remarkable sensing characteristics. This paper provides an exhaustive overview encompassing the production, functionalization strategies, and practical applications of gas sensors incorporating P3HT as the OSC layer. The exceptional sensing attributes and wide-ranging utility of P3HT position it as a promising candidate for improving PFET-based gas sensors.

Metal-Organic Framework Coated Devices for Gas Sensing

The demand for monitoring chemical and physical information surrounding, air quality, and disease diagnosis has propelled the development of devices for gas sensing that are capable of translating external stimuli into detectable signals. Metal-organic frameworks (MOFs), possessing particular physiochemical properties with designability in topology, specific surface area, pore size and/or geometry, potential functionalization, and host-guest interactions, reveal excellent development promises for manufacturing a variety of MOF-coated sensing devices for multitudinous applications including gas sensing. The past years have witnessed tremendous progress on the preparation of MOF-coated gas sensors with superior sensing performance, especially high sensitivity and selectivity. Although limited reviews have summarized different transduction mechanisms and applications of MOF-coated sensors, reviews summarizing the latest progress of MOF-coated devices under different working principles would be a good complement. Herein, we summarize the latest advances of several classes of MOF-based devices for gas sensing, i.e., chemiresistive sensors, capacitors, field-effect transistors (FETs) or Kelvin probes (KPs), electrochemical, and quartz crystal microbalance (QCM)-based sensors. The surface chemistry and structural characteristics were carefully associated with the sensing behaviors of relevant MOF-coated sensors. Finally, challenges and future prospects for long-term development and potentially practical application of MOF-coated sensing devices are pointed out.

Metal Organic Framework-Derived ZnO@GC Nanoarchitecture as an Effective Hydrogen Gas Sensor with Improved Selectivity and Gas Response

Although they are not as favorable as other influential gas sensors, metal-oxide semiconductor-based chemiresistors ensure minimal surface reactivity, restricting their gas selectivity, gas response, and reaction kinetics, particularly when functioning at room temperature (RT). A hybrid design, which includes metal-oxide/carbon nanostructures and passivation with specific gas filtration layers, can address the concerns of surface reactivity. We present a novel hierarchical nanostructured zinc oxide (ZnO), decorated with graphitic carbon (GC) and synthesized via a wet-chemical strategy, which is then followed by the self-assembly of a zeolitic imidazolate framework (ZIF-8). Because of its large surface area, high porosity, and efficient inspection of other analyte (interfering) gases, the ZnO@GC can provide intensified surface reactivity at RT. In the present study, such a hybrid sensor confirmed extraordinary gas sensing properties, which was characterized by excellent H₂ selectivity, fast response, rapid recovery kinetics, and high gas response (ΔR/R₀ ∼ 124.6%@10 ppm), particularly in extremely humid environments. The results reveal that adsorption sites provided by the ZIF-8 template-based ZnO@GC frameworks facilitate the adsorption and desorption of H₂.